Method of detecting cornering for an antilock regulation system

ABSTRACT

For cornering identification in an anti-lock control system and/or traction slip control system, wherein the rotational behavior of the wheels is measured and evaluated to determine a vehicle reference speed, and wherein criteria for cornering identification are derived from the wheel slip, the slip signals of the individual wheels are filtered and the signals sent are compared. Cornering is identified when simultaneously the filtered wheel slip on both front wheels is in excess of a predetermined maximum value and the filtered wheel slip values of one rear wheel exceed and that of the other rear wheel fall below a predetermined value. The threshold values depend on the vehicle reference speed. The direction of cornering is also identified.

BACKGROUND OF THE INVENTION

The present invention relates to a method of cornering identificationprovided for use in an anti-lock control system, wherein the rotationalbehavior of the vehicle wheels is measured by wheel sensors andevaluated to determine a vehicle reference speed which is used as areference value for ascertaining the wheel slip and for braking pressuremodulation, and wherein criteria for cornering identification and thedirection of cornering are derived from the wheel slip.

German patent No. 34 13 738 (P 5547) discloses a circuitry for ananti-lock brake system wherein for cornering identification the slipvalues on the wheels of one vehicle side are added and compared with theslip sum of the wheels of the other vehicle side, and the corneringidentification signal is produced as soon as the difference of the slipsums of both vehicle sides exceeds a predetermined limit value. In thebrake system concerned, the braking pressure variation in individualbraking pressure control channels is combined according to predefinedselection criteria, such as Aselect-low@ or Aselect-high@. The selectioncriteria and predetermined limit values which also influence the controlare changed when cornering is detected.

In an anti-lock system described in German patent application No. 21 19590, a cornering identification signal is produced by means of atransverse acceleration measuring device, for example, a mercury switch.

Further, German patent application No. 19 65 391 discloses an anti-lockcontrol system which determines the slip values of the individual wheelsand takes them into account for the braking pressure control.

Difficulties are involved in identifying cornering and adaptinganti-lock control to the different conditions prevailing during straighttravel and cornering. If the control data, as is conventional practicewith an anti-lock system, are produced exclusively or mainly by means ofwheel sensors, the wheel slip caused by cornering must be distinguishedfrom slip which is caused by locking tendencies or induced by thecontrol. Principally, it would be desired to take an information aboutstraight travel or cornering into account for the control. However, theuse of a steering angle sensor, transverse acceleration sensor, or thelike, which could supply such an information, is generally rejected forcost reasons. In more complex control systems, for example, in drivingstability control systems (DSC, ASMS), however, it is absolutelyimperative to bear the increased expenditure for sensors of theabove-mentioned type.

An object of the present invention is to achieve an exact corneringidentification in a simple fashion and without additional sensors, i.e.,only on the basis of the data supplied by the wheel sensors.

SUMMARY OF THE INVENTION

It has been found that this object can be achieved by the methoddescribed in accordance with the present invention, the special featuresof which involve that the wheel slip signals are filtered and thefiltered signals are compared and that Acornering@ is identified whensimultaneously the filtered wheel slip on the two front wheels is inexcess of a predetermined front-wheel-related maximum slip value that isresponsive to the instantaneous vehicle speed or vehicle referencespeed, and the filtered wheel slip of one rear wheel is above and thefiltered wheel slip of the other rear wheel is below a predeterminedrear-wheel-related maximum slip value that is responsive to the vehiclereference speed or below a predetermined minimum slip value responsiveto the vehicle (reference) speed, and the rear wheel having the lowerslip value or the higher speed is assessed as the curve-outward rearwheel to determine the direction of cornering.

When conventional circuitries, such as those of microcomputers and likeelements, and circuits or program steps having a low-pass filtercharacteristic are used, favorably, the filtered wheel slip signal isproduced according to the relation

    fws.sub.neu =fws.sub.alt +(fws.sub.alt -fws.sub.neu)/T

and >fws_(neu) = refers to the filtered wheel slip which was the lastone ascertained in the working cycle and >fws_(alt) = refers to thepreviously ascertained filtered wheel slip. >T= implies a predeterminedtime constant which ranges in the order between 30 and 200 msec, moreparticularly between 50 and 100 msec.

It is important to reliably distinguish between straight travel andcornering especially in relatively inexpensive anti-lock systems havingonly two hydraulically independent control channels or including theso-called 21/2 channel configuration in which the braking pressurecontrol in each of the two control channels is extended by an additionaltwo-way/two-position directional control valve. It is particularlyimportant in such 2-channel systems or 21/2 channel systems to adapt thecontrol to these special conditions during cornering identification.

The present invention utilizes the implication that the front wheelshave a slip responsive to the slip angle during cornering. This slipincreases with an increasing slip angle. The curve-inward rear wheel hasa smaller curve radius than the curve-outward rear wheel in a curve.Consequently, the curve-outward rear wheel is the wheel with the highestrotational speed and largely determines the vehicle reference speed. Thecloser the vehicle speed approaches the curve limit speed, the moredistinct and unambiguous this tendency becomes. This typical behavior isused for cornering identification according to the present invention.

In another preferred aspect of the method of the present invention, avalue in the order between 3 and 10% of the vehicle (reference) speed ispredetermined for the front-wheel-related maximum slip value, a value inthe order between 2 and 5% of the vehicle (reference) speed ispredetermined for the rear-wheel-related maximum slip value, and a valuein the order between 0.5 and 2% of the vehicle (reference) speed ispredetermined for the rear-wheel-related minimum slip value.

Further features, advantages and possible applications can be seen inthe following description, making reference to the accompanyingillustration of an embodiment of the present invention.

BRIEF DESCRIPTION OF THE DRAWING

The illustration is a schematic block diagram of a circuitry forimplementing the method of the present invention.

DETAILED DESCRIPTION OF THE DRAWING

The circuitry shown is included in an anti-lock system. Signalsrepresentative of the rotational behavior of the individual vehiclewheels are produced by means of wheel sensors S1 to S4. Generally,inductive transducers or active wheel sensors are used to date. Therepresented toothed discs 1 to 4, for example, are appropriate as signalgenerators. Toothed discs 1 to 4 rotate along with the vehicle wheelsand cause an alternating signal in the wheel sensors S1 to S4 whichcorresponds to the rotation and the number of teeth.

A conditioned speed signal v₁ to v₄ which corresponds to the wheel speedis produced from the sensor signals in a signal-conditioning circuit 5.

A vehicle reference speed V_(Ref) is produced in a circuit 6 bylogically combining the speed signals v₁ to v₄. Among others, thevehicle reference speed is used as a reference value to determine thewheel slip λ₁ to λ₄ of the individual vehicle wheels. To this end, thedifference between the vehicle reference speed v_(Ref) and therespective wheel speed v_(i) is produced according to the relation

    λ.sub.i =V.sub.Ref -v.sub.i

    (i=1 . . . 4).

The individual circuits to produce the wheel slip signals 8₁ to 8₄ arecombined and represented in a circuit block 7, as shown.

The wheel slip signals 8₁ to 8₄ are processed in a circuit 8 which is afilter with a low-pass characteristic. Generally, the relation

    fws.sub.i =λ.sub.i (1-e.sup.-t/T)

applies to a wheel i or, when a microcomputer and digital filteringtechnology is used, the relation

    fws.sub.neu =fws.sub.alt +(fws.sub.alt -fws.sub.neu)/T

applies individually to each wheel. >fws= herein designates the filteredwheel slip signal. >T= is the filter time constant which may rangebetween 30 and 200 msec, for example. In one embodiment, >T==70 msec.

The filtered wheel slip values fws are then analyzed in a corneringidentification circuit 9. ACornering@ exists when the followingconditions are simultaneously satisfied: ##EQU1## Indices 1 and 2 referto the front wheels, and indices 3 and 4 refer to the rear wheels.Comparison of the rear-wheel slip values indicates which rear wheel (therear wheel having the higher slip value) is the curve-outward wheel.

The slip thresholds S_(max) VA, S_(max) HA, S_(min) HA depend on thevehicle (reference) speed. In one embodiment of the present invention,the slip thresholds are defined as follows: ##EQU2## A simultaneousexceeding of the above-mentioned three threshold values permits reliablyidentifying cornering, and the direction of cornering can be identifiedby comparison of the rear-wheel slip values.

Thus, according to the present invention, the described logiccombination and evaluation of wheel rotational speeds or wheel slip dataof all vehicle wheels permits reliably and exactly distinguishingbetween straight travel and cornering. The control may then be improvedsignificantly on the basis of this information.

The above-mentioned dependence of the slip thresholds on the vehicle(reference) speed applies preferably only in a defined range or onlyabove a minimum vehicle (reference) speed. If necessary, it is possibleto change the slip percent values as a function of the vehicle speed.

In the embodiment shown, the output signals of the corneringidentification circuit 9 are sent to an ABS control logic 10 in whichthe proper determination or calculation of braking pressure modulationsignals is effected as a function of the rotational behavior of theindividual vehicle wheels. In addition, the data supplied by the curveidentification circuit are taken into account for anti-lock controloperations in the present case.

The output signals of the control logic are sent to a valve block 11which represents the various braking pressure control valves oractuators of an anti-lock control system. In an anti-lock hydraulicbrake system, for example, valve pairs (inlet and outlet valves) areassociated with the individual wheel brakes for anti-lock control.

The method for cornering identification and the described circuitryaccording to the present invention, which are preferably intended foruse in an anti-lock control system, are also appropriate for tractionslip control systems and other control systems where the objective is todistinguish between straight travel and cornering.

What is claimed is:
 1. A method of cornering identification for ananti-lock control system in a vehicle with two front wheels and two rearwheels, wherein the rotational behavior of the vehicle wheels ismeasured by wheel sensors and evaluated to determine a vehicle referencespeed which is used as a reference value for ascertaining wheel slipsignals and for breaking pressure modulation, and wherein criteria forcornering identification and the direction of cornering are derived fromthe wheel slip signals, wherein the wheel slip signals are filtered andthe filtered signals are compared, and wherein "cornering" is identifiedwhen simultaneously the filtered wheel slip signals on the two frontwheels are in excess of a predetermined front-wheel-related maximum slipvalue that is responsive to at least one of an instantaneous vehiclespeed and vehicle reference speed, and the filtered wheel slip signal ofone rear wheel is above a predetermined rear-wheel-related maximum slipvalue, and the filtered wheel slip of the other rear wheel is below apredetermined rear-wheel-related slip value that is responsive to thevehicle reference speed, and the rear wheel, having at least one of thelower slip value and the higher speed, is assessed as curve-outward rearwheel to determine the direction of cornering.
 2. The method of claim 1,wherein "cornering" is identified when the other rear wheel has a wheelslip signal below the predetermined rear-wheel-related maximum slipvalue.
 3. The method of claim 1, wherein "cornering" is identified whenthe other rear wheel has a wheel slip signal below a predeterminedrear-wheel-related minimum slip value.
 4. The method of claim 3, whereina value in the order between 0.5 and 2% of the vehicle reference speedis predetermined for the rear-wheel-related minimum slip value.
 5. Themethod of claim 1, wherein a value in the order between 3 and 10% of thevehicle reference speed is predetermined for the front-wheel-relatedmaximum slip value, and a value in the order between 2 and 5% of thevehicle reference speed is predetermined for the rear-wheel-relatedmaximum slip value.
 6. The method of claim 1, wherein at least oneprogrammed circuit and filter is provided having a low-pass filtercharacteristic and the filtered wheel slip signals are producedaccording to the relation

    fws.sub.neu =fws.sub.alt +(fws.sub.alt -fws.sub.neu)/T,

wherein "fws_(neu) " refers to the filtered wheel slip signal which wasthe last one ascertained in the working cycle, "fws_(alt) " refers tothe previously ascertained filtered wheel slip signal, and "T" implies apredetermined time constant which ranges in the order between 30 and 200msec.
 7. The method of claim 6, wherein the predetermined time constantranges in the order between 50 and 100 msec.